1. Field of the Invention
The present invention relates to an electro-mechanical energy conversion device more particularly, it relates to an electro-mechanical energy conversion device for a laminated type vibration driven motor or a pencil shaped type vibration driven motor and a manufacturing method for such a device.
2. Related Background Art
The laminated type vibration driven motor (hereinafter, simply referred to as a vibration driven motor or actuator) is constructed in a manner such that, as shown in FIG. 8, a disk-shaped stator 102 is attached to an edge of a shaft 101, a ring-shaped rotor 103 is pressure contacted to the upper surface of the stator 102, and when the shaft 101 executes a neck shaking motion while bending, the rotor 103 rotates due to a friction with the stator 102 (see U.S. Pat. Nos. 5,124,611 and 5,231,325).
FIGS. 9 and 10 show a specific structure of the conventional vibration driven motor. In the vibration driven motor, piezoelectric elements 104a to 104e which are stacked as five layers produce a neck shaking motion of the shaft 101. Each piezoelectric element 104 is divided into two portions and the polarizing directions in the thickness direction of the two divided portions of each piezoelectric element are opposite. When a voltage is applied, therefore, one of the two divided portions expands and the other contracts. When the direction of the voltage is changed, the expanded portion contracts and the contracted portion expands. In FIG. 10, the upper two piezoelectric elements 104a and 104b give a bending motion in the right/left direction to the shaft 101, the lower two piezoelectric elements 104c and 104d give a bending motion in the front/back direction to the shaft 101, and a neck shaking motion is executed by synchronizing those bending motions. The lowest piezoelectric element 104e is a piezoelectric element for detection of a resonance frequency in order to monitor a vibrating state of the motor.
According to the above vibration driven motor, as compared with the conventional ring-shaped vibration driven motor (see U.S. Pat. No. 4,580,073), the size and weight are 1/2 or less and the costs are 1/3 or less than those of the conventional motor. Therefore, a desired application of such device is to drive lenses of an automatic focusing single-lens reflex camera or the like in place of the ring-shaped vibration driven motor.
However, since the miniaturization of electronic parts progresses quickly, a further miniaturization of the laminated type vibration driven motor is demanded. In the above vibration driven motor, metal electrode plates 105a to 105d are used to apply AC voltages to produce the neck shaking motion. These electrode plates are respectively laminated to the laminated piezoelectric elements 104a to 104e so as to be inserted between the two piezoelectric elements. Therefore, a problem occurs in the realization of the miniaturization because of the thicknesses of the metal plates 105a to 105d and the complexity of electrode wirings.
When two kinds of AC voltages of different phases are applied to the piezoelectric elements, for example, in the case where it is necessary to apply a voltage of A volts to obtain a displacement of .lambda., it is known that the displacement of .lambda. can be obtained by setting a thickness of each piezoelectric element to 1/n and by applying the voltage of A/n volts to each of the laminated piezoelectric elements of n layers. That is, in order to drive at a low voltage, it is known that it is preferable to make the thickness of each piezoelectric element thin and to use a structure in which a number of such thin piezoelectric elements are laminated.
According to a method of manufacturing the conventional laminated type vibration driven motor mentioned above, however, a binder or the like is added to the piezoelectric powder and a green sheet obtained by molding is sintered and, after that, the resulting sintered green sheet is individually polarized. Therefore, when the thickness of the piezoelectric element is made so thin, the handling in each processing step is difficult, the number of metal plates for the electrodes each of which is inserted between the piezoelectric elements increases, and the miniaturization cannot be realized. A problem also occurs in the realization of low voltage driving of the elements for the laminated type vibration driven motor. The costs also rise.